Power operated rotary knives are widely used in meat processing facilities for meat cutting and trimming operations. Power operated rotary knives also have application in a variety of other industries where cutting and/or trimming operations need to be performed quickly and with less effort than would be the case if traditional manual cutting or trimming tools were used, e.g., long knives, scissors, nippers, etc. By way of example, power operated rotary knives may be effectively utilized for such diverse tasks as taxidermy; cutting and trimming of elastomeric or urethane foam for a variety of applications including vehicle seats; and tissue removal or debriding in connection with medical/surgical procedures and/or tissue recovery from a body of a human or animal donor.
Power operated rotary knives typically include a handle assembly and a head assembly. The head assembly includes an annular blade housing and an annular rotary knife blade supported for rotation by the blade housing. The head assembly of a power operated rotary knife also includes a gearbox housing which supports a gear train for rotatably driving the rotary knife blade. In some instances, the gear train supported in the gearbox housing may comprise a single gear, in other instances; the gear train may include a plurality of gears for driving the rotary knife blade. The gear train is part of a drive assembly for the power operated rotary knife, the gear train being internal to the rotary knife. Power operated rotary knives having various gear train embodiments including a gear train comprising a single gear and a gear train including a plurality of gears are disclosed in U.S. patent application Ser. No. 13/189,925 to Whited et al., filed on Jul. 25, 2011 (“the '925 application”). The '925 application is assigned to the assignee of the present application and is incorporated herein, in its entirety, by reference.
The drive assembly also includes components external to the power operated rotary knife including an external drive motor and a flexible shaft drive transmission. Motive or rotational power which drives the gear train of the power operated rotary knife is typically provided from an external drive motor and transmitted through a flexible shaft drive transmission. The flexible shaft drive transmission typically includes an elongated drive transmitting shaft which rotates within an outer casing. The elongated drive transmitting shaft includes a driven fitting at one end of the drive transmitting shaft that engages and is rotated by the mating drive fitting of the drive motor and a drive fitting at the opposite end of the drive transmitting shaft that engages and rotates a mating driven fitting of the gear train of the power operated rotary knife. Rotation of the drive transmitting shaft by the external motor rotates the gear train of the power operated rotary knife, which, in turn, rotates the rotary knife blade.
The outer casing of a typical flexible shaft drive transmission includes a first, motor end coupling at one end of the outer casing is adapted to be releasably coupled to a mating coupling of the drive motor, such that, when the motor end coupling and the drive motor coupling are engaged, the driven fitting of the drive transmitting shaft engages and is rotationally driven by the drive fitting of the drive motor. A second, handle assembly coupling at the opposite end of the outer casing is adapted to be releasably coupled to the handle assembly of the power operated rotary knife such that the drive fitting of the drive transmitting shaft engages and drives the driven fitting of the gear train of the power operated rotary knife.
In some prior flexible shaft drive transmissions, the drive interface or connection structure between the flexible shaft drive transmission and the drive motor was problematic. Typically, the first driven fitting of the drive transmitting shaft was a square male fitting that fit into a square female opening of the motor drive fitting. Such a square fitting connection between the drive transmitting shaft driven fitting and the motor drive fitting tended to be difficult to properly align for insertion when attempting to couple the first coupling of the outer casing to the motor coupling, often requiring the operator to use two hands to align and connect the shaft drive transmission and the drive motor. Additionally, over time, the vertices of the square male fitting of the drive transmitting shaft tended to become rounded off thereby resulting in a loose or sloppy drive connection between the mating drive fittings of the drive transmitting shaft and the drive motor. The loose or sloppy drive connection would often be characterized by an initial “clunking” from the drive connection when the drive motor was actuated by the operator to start the power operated rotary knife.
Furthermore, in some prior flexible shaft drive transmissions, there were alignment problems between the first coupling of the outer casing and the drive motor coupling resulting in axial misalignment between an axis of rotation of the drive fitting of the drive motor and an axis of rotation of the drive transmitting shaft or flex shaft of the flexible shaft drive transmission. Even a slight axial misalignment between the axis of rotation of the drive fitting of the motor drive and the axis of rotation of the drive transmitting shaft would result in undesirable vibration of the drive transmitting shaft and excessive wear of components of the flexible shaft drive transmission.
Additionally, in some prior flexible shaft drive transmissions, the first coupling of the outer casing included a rotatable or slip ring interposed between first coupling and the motor coupling to allow relative rotation between the first coupling and the motor coupling. Under certain conditions such as where the flexible shaft drive transmission was sharply angled because of the operator's positioning of the power operated rotary knife, the outer casing would tend to rotate at the drive motor end becoming “wound up” or twisted about the central longitudinal axis of the drive transmitting shaft. The presence of the slip ring also created sloppiness in the coupling connection between the flexible shaft drive transmission and the drive motor because of the combined tolerance build up of the first coupling, the slip ring, and the motor coupling. As noted previously, sloppiness in the flexible shaft drive transmission-motor coupling connection may lead to misalignment of the axis of rotation of the motor drive fitting and the axis of rotation of the drive transmitting shaft resulting in undesirable vibration of the drive transmitting shaft and excessive wear of components of the flexible shaft drive transmission.